The document summarizes the key components of a normal electrocardiogram (ECG). It describes that a normal ECG consists of P, QRS, and T waves. The P wave represents atrial depolarization, the QRS complex represents ventricular depolarization, and the T wave represents ventricular repolarization. It also outlines the placement of electrodes for the 12-lead ECG and which leads monitor different walls of the heart.

1. Dr. Abdulkadir Insi, MD

2. Characteristics of the Normal Electrocardiogram
• The normal electrocardiogram is composed of a P
wave, a QRS complex, and a T wave.
• The QRS complex is often, but not always, three
separate waves: the Q wave, the R wave, and the S
wave.
June 23, 2021 ECG intensive course for Medical Students 2

3. June 23, 2021 ECG intensive course for Medical Students 3

4. • Q wave is first downward deflection after P wave
• R wave is positive deflection after Q wave
• S wave is negative deflection after R wave
• T wave follows QRS
June 23, 2021 ECG intensive course for Medical Students 4

5. June 23, 2021 ECG intensive course for Medical Students 5

6. June 23, 2021 ECG intensive course for Medical Students 6

7. • The P wave is caused by electrical potentials
generated when the atria depolarize before atrial
contraction begins.
• The QRS complex is caused by potentials generated
when the ventricles depolarize before contraction,
that is, as the depolarization wave spreads through
the ventricles.
June 23, 2021 ECG intensive course for Medical Students 7

8. • Both the P wave and the components of the QRS
complex are depolarization waves.
• The T wave is caused by potentials generated as the
ventricles recover from the state of depolarization.
June 23, 2021 ECG intensive course for Medical Students 8

9. • This process normally occurs in ventricular muscle
0.25 to 0.35 second after depolarization, and the T
wave is known as a repolarization wave.
June 23, 2021 ECG intensive course for Medical Students 9

10. The Electrocardiogram (ECG)
■ An ECG is a series of waves and deflections
recording the heart’s electrical activity from a
certain “view.”
■ Many views, each called a lead, monitor voltage
changes between electrodes placed in different
positions on the body.
June 23, 2021 ECG intensive course for Medical Students 10

11. The Electrocardiogram (ECG)
■ Leads I, II, and III are bipolar leads, which
consist of two electrodes of opposite polarity
(positive and negative).
June 23, 2021 ECG intensive course for Medical Students 11

12. The Electrocardiogram (ECG)
■ Leads aVR, aVL, and aVF are unipolar leads and
consist of a single positive electrode and a
reference point (with zero electrical potential) that
lies in the center of the heart’s electrical field.
June 23, 2021 ECG intensive course for Medical Students 12

13. The Electrocardiogram (ECG)
■ Leads V1–V6 are unipolar leads and consist of a
single positive electrode with a negative reference
point found at the electrical center of the heart.
■ Voltage changes are amplified and visually
displayed on an oscilloscope and graph paper.
June 23, 2021 ECG intensive course for Medical Students 13

14. The Electrocardiogram (ECG)
■ An ECG tracing looks different in each lead because
the recorded angle of electrical activity changes with
each lead.
■ Several different angles allow a more accurate
perspective than a single one would.
June 23, 2021 ECG intensive course for Medical Students 14

15. The Electrocardiogram (ECG)
■ The ECG machine can be adjusted to make any skin
electrode positive or negative.
■ The polarity depends on which lead the machine is
recording.
June 23, 2021 ECG intensive course for Medical Students 15

16. The Electrocardiogram (ECG)
■ A cable attached to the patient is divided into
several different-colored wires: three, four, or
five for monitoring purposes, or ten for a 12-lead
ECG.
■ Incorrect placement of electrodes may turn a
normal ECG tracing into an abnormal one.
June 23, 2021 ECG intensive course for Medical Students 16

17. ♥ Clinical Tip
• Patients should be treated according to their
symptoms and signs, not merely their ECG.
• To obtain a 12-lead ECG, four wires are attached to
each limb and six wires are attached at different
locations on the chest.
• The total of ten wires provides twelve views (12
leads).
June 23, 2021 ECG intensive course for Medical Students 17

18. Limb Leads
June 23, 2021 ECG intensive course for Medical Students 18

19. Limb Leads
• Electrodes are placed on the right arm (RA), left
arm (LA), right leg (RL), and left leg (LL).
• With only four electrodes, six leads are viewed.
■ Standard leads: I, II, III
■ Augmented leads: aVR, aVL, aVF
June 23, 2021 ECG intensive course for Medical Students 19

20. Standard Limb Lead Electrode Placement
June 23, 2021 ECG intensive course for Medical Students 20

21. Standard Limb Leads
June 23, 2021 ECG intensive course for Medical Students 21

22. Elements of Standard Limb Leads
June 23, 2021 ECG intensive course for Medical Students 22

23. Augmented Limb Leads
June 23, 2021 ECG intensive course for Medical Students 23

24. Elements of Augmented Limb Leads
June 23, 2021 ECG intensive course for Medical Students 24

25. ECG patterns of the six standard leads
June 23, 2021 ECG intensive course for Medical Students 25

26. 12-Lead ECG
oInferior Wall:
• Leads II, III, aVF
Left Leg
June 23, 2021 ECG intensive course for Medical Students 26

27. oLateral Wall:
• Leads I and aVL
Left Arm
June 23, 2021 ECG intensive course for Medical Students 27

28. Chest Leads
June 23, 2021 ECG intensive course for Medical Students 28

29. Standard Chest Lead Electrode Placement
June 23, 2021 ECG intensive course for Medical Students 29

30. Elements of Chest Leads
June 23, 2021 ECG intensive course for Medical Students 30

31. oSeptal Wall:
Leads V1, V2
• Along sternal borders
June 23, 2021 ECG intensive course for Medical Students 31

32. oAnterior Wall:
• V3, V4
Left anterior chest
June 23, 2021 ECG intensive course for Medical Students 32

33. • Lateral Wall:
oLeads V5 and V6
•Left lateral chest
June 23, 2021 ECG intensive course for Medical Students 33

34. June 23, 2021 ECG intensive course for Medical Students 34